The invention relates to a method of assessing interfering noise in motor vehicles. Noises of this type occur, for example, during a rubbing motion of material surfaces.
In connection with the diagnosis of motor vehicle functions, a method of determining an adhering-sliding motion is known from German Patent document DE 197 23 728 A1. This known method relates essentially to the capability to differentiate between a normal condition and an adhering-sliding of moving working elements, such as control valves.
Furthermore, a method of determining components of a vehicle unit which are in need of repair is known from German Patent document DE 34 37 661 A1. In the case of this method, vehicle units are measured in the new condition with respect to occurring vibrations. Particularly during later maintenance work, the same vehicle unit is measured again with respect to occurring vibrations. The intensities of the vibrations are compared with one another. A disproportionately high increase of the intensity of a vibration is a criterion of the need of a component to be repaired. In this case, comparative measurements can be made only in the case of one and the same vehicle unit. Furthermore, in that case, not all interference noises which may occur in a vehicle unit can be diagnosed.
From German Patent document DE 33 32 941 A1, an overall sound analysis of running machines and systems is generally known, during which the recorded sounds are compared with defined threshold values,
In U.S. Pat. No. 5,551,298, various components are caused to vibrate as a result of defined vibration excitations. The recorded vibrations are assessed by means of stored vibrations with respect to their frequency or frequency band in order to identify the source of a noise in the form of a certain component. Here also, only a limited diagnosis of the noise source can be made.
From the Japanese abstract of Japanese Patent document JP 10246689 A, a machine is known by which the rubbing noise of a material can be determined.
Finally, from German Patent document DE 199 26 411 C1, a method is known for determining the cause of interfering noises in motor vehicles. Especially for noises caused by an adhering-sliding movement on material surfaces, this method suggests to store this noise relative to the contact site of the materials.
The previous methods relate to the problem of identifying the cause of interfering noises of different components in the motor vehicle. Different components are diagnosed in different fashions.
It is an object of the invention to provide an improved a method of the above-mentioned types in the sense of a standardized systematology.
This object is achieved by providing a method of assessing interfering noises in motor vehicles. The noises occurring during a defined measuring time are divided into different frequency ranges. Within the frequency ranges, the level changes are determined with respect to the background noise. The thus determined level changes are analyzed. Advantageous further developments of the invention are described and claimed herein.
In the case of the method according to the invention for assessing interfering noises, no differentiation is made between the different possibilities of generating noise (for example, an exclusive adhering-sliding motion of material surfaces). To the contrary, the entire noise spectrum-independently of its origin—is examined over the defined measuring time. Advantageously, for this purpose, the signal is stored over the measuring time and is analyzed isochronously.
In contrast to a method for determining a subjectively perceived noise, as known from German Patent document DE 198 44 784 A1, in the case of the invention, there is no leaving of the time domain when analyzing the interfering noises. In contrast, in the case of the known method, a transformation takes place into the frequency range. Apart from the fact that in this case also possibly interfering noise is treated in the same manner and is therefore changed, as a result of the inertia typical of a frequency-dependent analyzing method, such a method is not exactly capable of differentiating between high-frequency interfering noises and the background noise level.
In the case of the invention, the analysis of the interference noises takes place frequency-range-selectively. For this purpose, the noises are divided into various frequency bands. Within the frequency bands, the level changes are defined with respect to the background noise and the thus determined level changes are analyzed.
In order to determine the background noise, the noises are scanned within their frequency range with first time windows and are averaged over the first time window.
In this case, the first time windows for the frequency ranges can mutually have the same duration. As a result, a uniform basis is created, particularly for a joint taking-into-account of the noise events in the different frequency bands.
For determining the unsteady noise fraction within its frequency range, the noises can be scanned with second time windows whose duration is shorter than that of the first time windows. This examination possibility can be conducted at low technical expenditures.
In this case, the second time windows may have a shorter time duration for the range of higher frequencies than for the range of lower frequencies. As a result, the interfering-noise sensitivity of human hearing is taken into account, which differs as a function of the frequency range.
The level change frequency of unsteady noise events is defined from the unsteady noise fraction. The level change will be registered when it exceeds a defined threshold.
In a supplementary fashion, the level change amplitudes of unsteady noise events can be determined from the unsteady noise fraction. The intensity of the interfering noises can thereby be detected.
An overall assessment of the noise and a differentiation between an acceptable and an unacceptable noise behavior can be achieved in a particularly simple manner when a weighted sum of the level change frequencies and of the level change amplitudes is formed over all frequency ranges.
As a result, a method is obtained for assessing interfering noises which supplies objective information concerning interfering noises.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.